The present invention relates generally to eddy current inspection probes for inspecting a surface of a manufactured component, and more particularly to a probe having an improved fit with the surface of the component.
Eddy current inspection is commonly used to detect flaws in surfaces of manufactured components such as gas turbine engine components. During this type of inspection, electromagnetic induction is used to induce eddy currents in the component being inspected. An array of coils inside an eddy current probe generates alternating magnetic fields which induce the eddy currents in the component when the probe is moved near the component. When flaws are present in the component, the flow of eddy currents is altered. The altered eddy currents produce changes in a secondary magnetic field which are detected by the array of coils inside the eddy current probe. The array generates an electrical signal in response to the altered secondary magnetic field. The amplitude of the electrical signal is generally proportionate to the size of the flaw. Thus, approximate sizes and general locations of flaws,may be determined using eddy current probes.
The array must be kept at a constant distance from the surface of the component being inspected to ensure the amplitude of the electrical signal is proportionate to flaw size. One way of ensuring a constant distance is by sizing and shaping the probe substantially identically to the feature being inspected. For instance, if the surface of an opening in a gas turbine engine disk such as a dovetail slot bottom is being inspected, a probe sized and shaped substantially identically to the opening is used.
Frequently, the probe is made to collapse so it can fit into the opening. These collapsible probes generally have an expandable core inside a flexible covering which holds the array. In the past, the covering was bonded to the core. As a result, the covering stretched and distorted as it expanded. Changes in the probe shape prevented the array from being positioned at a uniform distance from the surface being inspected. Further, due to variations in size and shape of the actual features being inspected, gaps sometimes occurred between the probe and the surface which also prevented the array from being positioned at a uniform distance from the surface being inspected.
Among the several features of the present invention may be noted the provision of an eddy current inspection probe for inspecting a preselected surface at least partially defining an opening in a component. The eddy current inspection probe comprises a cast core having an exterior surface sized and shaped for receipt within the opening of the component. The core is resiliently deformable between a retracted position for inserting the probe into and removing the probe from the opening in the component and an expanded position in which the probe is sized and shaped for at least partially filling the opening and contacting the preselected surface of the component for inspecting the surface. Further, the probe includes an eddy current array positioned over the exterior surface of the core for generating and detecting magnetic fields in the component to inspect the preselected surface of the component. The eddy current array has an outer surface shaped substantially identically to the preselected surface of the component when the core is in the expanded position for maintaining the outer surface of the array a preselected distance from the surface of the component.
In another aspect, the present invention includes a method of making a core for an eddy current inspection probe. A polyurethane epoxy is mixed and poured into a mold shaped for producing the core. The mold is opened after a period of time sufficient for the epoxy to cure, and the core is removed from the mold.
In yet another aspect of the present invention a core having an exterior surface sized and shaped for receipt within the opening of the component is molded, and an element is positioned over the exterior surface of the core. A compliant covering is positioned over an outer face of the element. An eddy current array is positioned over the covering for generating and detecting magnetic fields in the component to inspect the preselected surface of the component.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.